People who indicated in long-form questionnaire Item 20a that they had served on active duty in the past (civilian veterans) or were on active duty at the time of enumeration were asked to indicate in Question 20b the period or periods in which they served. People who served in both wartime and peacetime periods are tabulated according to their wartime service.

The responses to the question about period of service were edited for consistency and reasonableness. The edit eliminated inconsistencies between reported period(s) of service and the age of the person; it also removed reported combinations of periods containing unreasonable gaps (for example, it did not accept a response that indicated that the person had served in World War II and in the Vietnam era, but not in the Korean conflict).

The data on veteran status were derived from answers to long-form questionnaire Item 20a. For census data products, a "civilian veteran" is a person 18 years old and over who, at the time of the enumeration, had served on active duty in the U.S. Army, Navy, Air Force, Marine Corps, or Coast Guard in the past (even for a short time), but was not then on active duty, or who had served in the Merchant Marine during World War II. People who had served in the National Guard or Military Reserves were classified as veterans only if they had ever been called or ordered to active duty, not counting the 4 to 6 months for initial training or yearly summer camps. All other civilians 18 years old and over were classified as nonveterans.